Revenue Recognition- Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 30, 2018	Mar. 31, 2017
Revenues	$ 96,457,000	$ 84,122,000
Deferred Revenue, Revenue Recognized	2,604,000
Engineering and Other Scientific [Member] \| Time And Materials Contracts [Member]
Revenues	64,557,000
Engineering and Other Scientific [Member] \| Fixed Price Contracts [Member]
Revenues	12,446,000
Environmental and Health [Member] \| Time And Materials Contracts [Member]
Revenues	18,614,000
Environmental and Health [Member] \| Fixed Price Contracts [Member]
Revenues	840,000
Sales Revenue, Net [Member] \| Time And Materials Contracts [Member]
Revenues	$ 83,171,000
Concentration Risk, Percentage	86.00%
Sales Revenue, Net [Member] \| Fixed Price Contracts [Member]
Revenues	$ 13,286,000
Concentration Risk, Percentage	14.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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Amount of revenue recognized that was previously reported as deferred or unearned revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response))
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
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